1. Field of the Invention
The present invention relates to a liquid crystal display apparatus, further particularly to a liquid crystal display apparatus having advantages that it provides high brightness, a reduced thickness, while removing bright lines and waterfall and lowering a manufacturing cost.
2. Description of the Related Art
A liquid crystal display is a display device using a liquid crystal cell for modification of light, or a device turning variation of optical property such as birefringence, circumpolarization, dichroism, and light scattering caused by rearrangement of liquid crystal particles into visual variation by applying voltage to the liquid crystal particles having a particular arrangement.
The liquid crystal display apparatus requires an additional light source or a back light assembly to emit light onto a liquid crystal display panel because the liquid crystal display apparatus is a light receptive display apparatus displaying by adjusting an amount of the light received from outside. Herein, the liquid crystal display apparatus is divided into an edge-type liquid crystal display apparatus and a direct-down type liquid crystal display apparatus according to a structure of the back light assembly.
First of all, the edge-type back light assembly of the liquid crystal display apparatus comprises a lamp installed on sides of a light guide plate guiding the light, and is usually used in a small-size liquid crystal display apparatus such as a monitor for a laptop computer or a desktop computer because it does not have as good brightness in a big-size LCD as the direct-down type back light assembly has, even though it has advantage that it has a good homogeneity of the light, long durability, and good adaptability to flattening of the liquid crystal display apparatus.
Meanwhile, the direct-down type back light assembly is mainly used for the liquid crystal display apparatus having a big screen requiring a high brightness because of higher utilization efficiency of the light compared to the edge-type back light assembly.
Hereinbelow, a conventional direct-down type liquid crystal display apparatus will be described. Also, a rear will refer to a direction toward a reflector, while a front will refer to a direction toward a liquid crystal display panel unless described otherwise.
As illustrated in FIG. 1, a conventional direct-down type liquid crystal display apparatus 100 comprises a liquid crystal display panel 110 displaying a picture, a back light assembly 120 provided on the rear of the liquid crystal display panel and emitting the light onto the liquid crystal display panel 110, a PCB (printed circuit board) 140 transferring a visual signal to the liquid crystal display panel 110, and a front chassis 160 covering front edges of the liquid crystal display panel 110.
The liquid crystal display panel 110 comprises a first panel 114 formed with a switching component like a TFT (thin film transistor) and with a pixel electrode, a second panel 112, and a liquid crystal (not shown) inserted between the first panel 114 and the second panel 112. Herein, a visual signal applied by the PCB 140 is transferred to a thin film transistor on the first panel 114 via a drive IC (not shown). Accordingly, the liquid crystal applied with an electric signal displays a picture using the light emitted from the back light assembly 120.
The back light assembly 120 comprises a lamp 121 emitting the light, a reflector 122 installed on the rear of the lamp 121, an optical sheet layer 123 having a diffusion plate 123a and a prism sheet 123b provided above the lamp 121 and being spaced from the reflector 122, and a supporting frame 124 accommodating and supporting the reflector 122 and the optical sheet layer 123.
The reflector 122 is installed on the rear of the optical sheet layer 123 and spaced from the optical sheet layer 123. Further the plurality of lamps 121 are installed on the front side of the reflector 122. The reflector 122 can minimize loss of the light by reflecting part of the light emitted from the lamp 121 to the rear toward the optical sheet layer 123.
The supporting frame 124 comprises a front frame 126 covering the front edges of the optical sheet layer 123, and a rear supporting frame 125 combined on the rear of the front frame 126 and accommodating and supporting the optical sheet layer 123 and the reflector 122 in an accommodating space formed between the front frame 126 and the rear frame 125.
Meanwhile, the liquid display panel 110 is installed on the front of the supporting frame 124 to closely support rear edges of the liquid display panel 110. Also, an inverter (not shown) inverting a direct current supplied from the outside into an alternating current to supply the alternating current to the lamp 121 is provided on the rear of the reflector 122.
The PCB 140 is connected to the first panel 114 with a FPC (flexible printed circuit) 150. The FPC 150 connected to the first panel 114 is folded twice at each corner on inside of the supporting frame 124 to install the PCB 140 connected to the other end of the FPC 150 on the rear of the rear frame 125.
Meanwhile, the conventional direct-down type liquid crystal display apparatus 100 has following disadvantages.
Firstly, as illustrated in FIG. 2, the conventional direct-down type liquid crystal display apparatus 100 has the disadvantage that bright lines occur on an area “a” on the direct front of the lamp 121 becomes brighter than an area “b” on the front of a space positioned between the lamps 121.
Secondly, to prevent the bright lines caused by difference of the brightness of each lamp 121, a distance “Q” between the lamp 121 and the optical sheet layer 123 has to be increased, which makes the flattening of the liquid crystal display apparatus 100 hard. Also, in case that a distance “P” between the lamps 121 is decreased, it may prevent occurrence of the bright lines on the liquid crystal display panel 110, however it has disadvantages that it increases a manufacturing cost and consumes more power.
Thirdly, in the conventional direct-down type liquid crystal display apparatus 100, the lamp 121 on the rear of the optical sheet layer 123 radiates heat as well as it emits the light. The heat radiated from the lamp 121 deteriorates the liquid crystal display panel 110 and the optical sheet layer 123 and, as a result, it decreases the brightness of the liquid crystal display apparatus 100 due to the heat. FIG. 3 illustrates variation of the brightness according to passage of time during an operation of the conventional direct-down type liquid crystal display apparatus 100. Here, “A” in FIG. 3 represents the variation of the brightness of the lamp 121 according to the passage of the time, and “B” in FIG. 3 represents the variation of the brightness of liquid crystal display apparatus 100 measured when it is assembled completely. It can be inferred that decrease of the brightness by the deterioration of the LCD panel 110 or the optical sheet layer 123 is more intensified when the liquid crystal display apparatus 100 is assembled completely than decrease of the brightness of the lamp 121 itself when it is not assembled.
Fourthly, it has disadvantage that waterfall occurs on the liquid crystal display panel 110 by mutual interference on an area where a driving frequency of the lamp 121 and a driving frequency of the inverter are similar to each other when the inverter is installed on the rear of the reflector 122 which is close to the rear of the lamp 121 to operate the lamp 121. A ITO (indium tin oxide) sheet 123c is installed on the front of the diffusion plate 123a to solve the problem, however, low transmittivity of the ITO sheet 123c decreases the brightness of the liquid crystal display apparatus 100, increasing the manufacturing cost of the liquid crystal display apparatus 100.
Fifthly, in the direct-down type liquid crystal display apparatus 100, the front chassis 160 and the supporting frame 124 should be disassembled to open and replace a broken lamp among the plurality of lamps 121.